In order to improve air environment, it is an important object to reduce nitrogen oxides (NOx), suspended particulate matter (SPM), and the like discharged from diesel-powered automobiles. As a method for reducing these pollutants, it is considered to be effective to mount an exhaust gas-treating apparatus on the diesel-powered automobiles. However, since the exhaust gas-treating apparatus is frequently less resistant to sulfur, it is desirable to reduce sulfur content contained in a fuel oil (light gas oil) to a large degree in order to efficiently function the apparatus. Thus, in order to cope with these requests, various desulfurization catalyst technologies having an excellent desulfurization performance have been proposed (e.g., see Patent Documents 1 and 2).
With regard to the properties of the light gas oil to be used as a fuel oil for the diesel-powered automobiles, low-temperature fluidity is also an important factor in addition to the sulfur concentration. In the light gas oil fraction where sulfur reduction is achieved by a general hydrotreatment method, there is a tendency that wax matter is apt to precipitate at a low temperature and thus low-temperature fluidity performance decreases. Thus, as one method for compensating the decrease, it is considered that a kerosene fraction is mixed with the light gas oil fraction to enhance the low-temperature fluidity performance and thus practical performance as a product light gas oil is secured.
However, since demand for the kerosene fraction increases in winter where the low-temperature fluidity performance is more desired, the use of the kerosene fraction for securing the low-temperature fluidity performance of light gas oil is not preferred in view of the balance of supply and demand. Accordingly, there has been strongly requested a catalyst capable of ultra-deep desulfurization of the light gas oil fraction and also having dewaxing activity which enables enhancement of the low-temperature fluidity performance so as to be sufficient for reducing the mixing amount of the kerosene fraction at production of product light gas oil.
As a method for performing dewaxing and desulfurization of the light gas oil fraction simultaneously, there has been proposed a method for dewaxing and desulfurization of a light gas oil fraction using two kinds of catalysts, wherein the light gas oil fraction is first brought into contact with ZSM-5 type zeolite which may contain a hydrogenation component to achieve dewaxing treatment and subsequently desulfurization treatment is performed with a conventional hydrodesulfurization catalyst (e.g., see Patent Document 3).
In addition, as a technology aiming at improvement of both of desulfurization performance and dewaxing performance which targets not the light gas oil fraction but mainly a heavy oil, there has been proposed a catalyst mixing ZSM-5 type zeolite and a specific support and containing oxides or sulfides of the metal in Group 6 and the metal in Group 8 (e.g., see Patent Document 4).
Patent Document 1: WO2004/054712
Patent Document 2: WO2003/000410
Patent Document 3: JP-A-50-17401
Patent Document 4: JP-A-59-132942